This application is 371 of pending international application PCT/EP98/03601 filed on Jun. 15, 1998.
1. Field of the Invention
The present invention relates to a medical gear pump for suction and irrigation, in particular for endoscopy or the laboratory, comprising two meshing gears as conveying elements, one of which is joined to a drive mechanism, the gears being received in cylindrical openings of a pump housing and the openings being connected to an inlet and to an outlet, the gears being received in non-journal-mounted fashion in the openings and the two gears each being equipped with a helical tooth set.
2. Related Prior Art
A gear pump of this kind for homogenizing medical, cosmetic, and technical products and mixtures is known from German Utility Model No. 18 22 807.
It is possible for gears mounted in non-journal-mounted fashion to seal themselves with respect to the housing wall during operation as a result of the differential pressure of the pump.
In German Utility Model No. 18 22 807, coupling of the doubly ball-bearing-mounted drive shaft to the directly drive gear is accomplished by way of an oval stem end that is inserted into an oval bore in the driven gear. This primarily serves the purpose of better emulsification, since the eccentric freedom of movement of the directly driven gear with respect to the drive shaft is one-dimensional and co-rotates. Consistent sealing, over the entire rotation, of the tooth tips in the cylindrical bore in which the gears are received is thereby prevented, since because of its eccentricity, the directly driven gear is lifted to some extent out of its self-sealing position twice during each rotation. To ensure smooth operation, a mounting system for the pump drive shaft that is impact-damped using rubber rings is therefore provided.
A similar bearing system for the driven shaft is known from German Utility Model No. 18 21 554.
A gear pump of this kind for delivering highly aggressive media is known from German Utility Model No. 19 75 041.
It is known from DE 83 31 598 U1 to additionally provide irrigation conduits.
When a pump of this kind is used in the medical field, the actual conveying means, i.e. the gears and the corresponding flow conduits, come into contact with the medical liquids, thus posing the problem of cleaning and disinfection.
The pumps that have become established in the medical field are therefore primarily peristaltic ones, in which the medical liquids are transported by rollers which act externally on flexible tubes.
Although it is possible thereby to ensure that the actual conveying elements do not come into direct contact with the medical liquid, the resulting conveyed flow is nevertheless a pulsating flow, which is not especially suitable, in particular, for applications in hysteroscopy, urology, and arthroscopy.
It is therefore the object of the present invention to create a medical pump which on the one hand is of simple design and also easy to clean, and moreover supplies a continuously variable controllable conveyed flow with high pump efficiency.
According to the present invention, the object is achieved in that in the case of the gear pump cited initially, the helical tooth set of the gears is configured such that, when viewed along a surface line of the gears, at least two tooth tip/root contact points of the meshing gears are present; and the contour of the tooth spaces of the one gear is matched to the teeth of the other gear in such a way that when a tooth has completely penetrated into the tooth space, its tooth tip almost completely fills up the tooth space radially inside the pitch circle.
The fact that at least two tooth tip/root contact points of the meshing gears are present along a surface line ensures precise concentricity of the meshing gears without wedging forces. The driven gear is in meshing engagement, continuously and in exact alignment, with the undriven non-journal-mounted gear. This eliminates the risk that the undriven gear will come into contact with edges or corners of the overlapping cylindrical housing bores. Coordination of the contours of the tooth spaces and teeth, in such a way that a tooth that has penetrated completely into the tooth space almost completely fills up the latter, on the one hand ensures that only an extremely small cavity volume, i.e. almost no volume at all, is present between the tooth space and tooth and is filled with liquid, and thus only extremely small quantities of liquid can be transported back at all, so that pump output efficiency is maintained at high rotation speeds. If greater quantities were transported back at high rotation speeds, pump output efficiency would be greatly reduced. In addition, this configuration creates outstanding sealing between the delivery and intake sides of the pump.
As a result of the helical tooth set in conjunction with the two-point contact and the particular configuration of the tooth and tooth space, the flow conduit which is necessarily present between the meshing teeth is sealed in such a way that any out-flow through it is efficiently prevented.
It is possible with this special configuration, in the case of meshing gears having a helical tooth set, to dispense with a central journal bearing arrangement for the two gears. The axial bearing points in the conveying chambers which receive the gears are accordingly also omitted. The result is not only to eliminate numerous niches for bacteria, which are difficult to clean and disinfect, but assembly and disassembly are also very simple, since for assembly the gears simply need to be placed into the conveying chamber, with no need to ensure that pivot bearing journals are inserted into a specific bearing point. The special helical tooth set not only results in very quiet-running gears, so that the operator is not disturbed by loud pump noises, but leads to consistently exact meshing engagement with the drive gear. The two gears are received, with a slight radial clearance, in approximately cylindrical overlapping openings. The diameter of the cylindrical openings is thus slightly greater than the diameter of the addendum circle of the respective gears. When the pump according to the invention is then operated with the non-journal-mounted gears, the relative overpressure on the delivery side causes the undriven gear to be displaced somewhat toward the intake side. In other words, during operation, the gears move slightly out of coaxial alignment in the approximately cylindrical chamber in which the respective gear is received. The result of this, when considering the addendum circle of the undriven gear, is an approximately half-sickle-shaped region, widening toward the delivery side, between the addendum circle and the circular inner wall of the conveying chamber in which that gear is received.
This region on the one hand ensures that transfer of the conveyed liquid of a tooth space from the intake pressure state to the outlet pressure is accomplished extremely smoothly, especially in conjunction with the helical tooth set and the configuration of the teeth, resulting not only in extremely quiet conveying but also in a transition from the tooth space to the pressure level with no loss of pressure. The combination of sickle and helical tooth set yields particularly harmonious, smooth, and thus also quiet conveying.
Because of the sickle-shaped region opening toward the delivery side, a force component is created which pushes the undriven gear toward the driven gear. This movement of the meshing gears toward one another results, in combination with the particular configuration of the teeth, in outstanding sealing between these gears, so that a self-sealing effect can be achieved. Backflow from the teeth as they come out of engagement, which impairs pump efficiency, is thereby greatly minimized. This is because the meshing teeth come out of engagement in a direction opposite to the inlet; i.e. quantities of liquid caught between the tooth space and tooth would be conveyed against the conveying direction, which can greatly impair pump output efficiency.
In production engineering terms, this has the considerable advantage that there is no need to produce highly precise parts to tight tolerances, but rather that a relatively wide tolerance range is available so that economical production methods are possible. This also opens up the possibility, for example, of manufacturing the gears from plastic materials, and optionally providing them for one-time use.
The good sealing attained by way of the working principle of the invention, and less by way of high precision in parts production, also results in a correlation between the pressure/flow characteristics diagram, the torque/speed characteristics field, and the current/voltage characteristics diagram that is more reproducible than with usual gear pumps. This allows these characteristics diagrams to be determined once on one production unit; these matrix values can then be used for pressure and flow control, eliminating direct outlet pressure measurement (which is associated with a certain complexity).
In a further embodiment of the invention, a pump body is provided which is detachably joined to a drive body, the inlet, cylindrical openings with gears, and outlet being arranged in the pump body.
This feature has the considerable advantage that for cleaning and disinfection, the pump body is removed from the drive body and the components which come into contact with medical liquids, i.e. the inlet, conveying chambers, gears, and outlet, are present in one and the same component, namely in the pump body, which can then be correspondingly cleaned and disinfected.
In a further embodiment of the invention, the pump body is configured so that it can be placed onto the drive body.
This feature has the advantage that handling during disassembly and assembly is particularly simple, i.e. for example, after being used the pump body simply needs to be removed from the drive body, which is very easy and can be performed by even untrained persons.
In a further embodiment of the invention, the pump body is joinable to the drive body via a bayonet coupling.
This feature has the advantage that a bayonet coupling is very easy to close and open, and at the same time ensures the appropriate sealing contact pressure between pump body and drive body.
In a further embodiment of the invention, the pump housing is configured as a solid plastic part in which the cylindrical openings are recessed in such a way that the gears can be inserted into the cylindrical openings from one side of the pump housing.
This feature has the considerable advantage not only that the pump housing can be manufactured as an economical part, for example an injection-molded part, but also that installation of the gears in the pump housing is very easy: they simply need to be pushed in or out once the pump cover has been pulled off. The plastic part can be manufactured as a mass-produced item, so that it can be configured as a disposable part, i.e. the pump body is discarded after a single use, and a new pump body is simply placed onto the drive body.
In a further embodiment of the invention, there projects from the driven gear a coupling stem which is insertable into a corresponding coupling counterelement of a motor in the drive body.
This feature has the advantage that the nonpositive connection between the drive mechanism and the driven gear can be created very easily by way of the push-in coupling.
In a further embodiment of the invention, an intermediate pin is arranged between the coupling stem and motor.
This feature has the advantage that the gear, with its drive stem, can be easily removed and replaced by removing the pump cover, for example via a bayonet coupling. Because of its replaceability, the intermediate pin with its double-articulated effect also has the advantage that different coupling diameters can be used for single-use and multiple-use pump versions. This makes it possible to injection-mold the drive stem along with the gear as a unit for the single-use version, and for the multiple-use versions to anchor into the driven gear a stainless, hardened, and sufficiently strong steel stem with a small outside diameter. A small outside stem diameter results in a lower circumferential speed at the corresponding sealing lip, and this in turn results in less wear on the stem seal.
In a further embodiment of the invention, the coupling between the coupling stem and motor is configured as a slot coupling.
This feature has the advantage that the coupling is self-aligning, i.e. regardless of the relative rotational position of the coupling stem and coupling counterelement, alignment is accomplished and any shaft offset is compensated for.
Thus by simply placing the pump body onto the drive body, the coupling between motor and driven gear can simultaneously also be aligned and closed.
In a further embodiment of the invention, a stoppage sealing valve is arranged in the outlet.
This feature has the advantage that when the pump is stopped, no backflow can occur in either direction. If the pump is being used, for example, as an irrigation pump, it is usually conveying from a reservoir vessel located higher up, so that it is then possible to ensure in particular that no backflow or over-flow can occur through the pump.
In a further embodiment of the invention, the stoppage sealing valve is configured as a ball-type nonreturn valve.
This feature has the advantage that the outlet can be blocked to prevent backflow or outflow during a stoppage using only a few components, for example a spring-loaded ball, components which can easily be assembled, disassembled, and cleaned.
In a further embodiment of the invention, the stoppage sealing valve is configured as a slit body made of flexible material that is arranged in the cross section of the outlet.
A passive stoppage sealing valve of this kind can be configured, for example, by way of a simple cross-slit silicone disk. The outside diameter of the slit disk corresponds to the outside diameter of a pump outlet tube. The diameter of the peripheral circle of the crossed slits in the disk corresponds to the inside diameter of the pump outlet tube. The disk is simply held immovably between the end surface of the pump outlet tube introduced into the housing outlet bore and the inner stop surface of the housing outlet bore. The differential pressure for the transition from stoppage sealing to flow can be adjusted by way of the disk thickness and/or the Shore hardness of the silicone disk.
In a further embodiment of the invention, the stoppage sealing valve is configured as a magnetically driven plunger, connected in parallel with a motor of the drive mechanism, which can be extended in blocking fashion into the cross section of the outlet when the motor switches off.
The advantage of this function is that an active stoppage shut-off valve is created. A flat plunger, not belonging externally to the replaceable pump body, acts, through a matching slot of the pump housing in the region of the housing outlet bore, on a relatively thin-walled silicone tube introduced there. In one linear end position of the plunger the flow is sealedly shut off; in the other linear end position the full flow is possible without a pressure loss. The housing slot and the nonrotatable plunger edge are configured so that regardless of the linear stroke position of the edge, the pump body can unimpededly be put in place or removed with a quarter-turn in bayonet fashion. The outside diameter of the thin-walled tube is somewhat larger than the diameter of the housing outlet bore. It is inserted via vacuum finger, and thereafter is sealed without adhesive bonding in all operating states of the housing bore.
In a further embodiment of the invention, an overpressure valve is provided which, in the event of overpressure, moves a pump cover relative to the pump housing in such a way that even though the drive mechanism is running, what occurs is not conveyance but rather backflow to the inlet.
This feature has the advantage that overpressure situations can be regulated with relative simple measures. In an overpressure situation, the pump cover is moved so as to create an opening from the outlet toward the inlet, so that the pump conveys back toward the inlet in circulating fashion.
In a further embodiment of the invention, an overpressure valve spring with plunger is provided in the drive body, and in an overpressure situation allows the pump cover to tilt away from the pump housing on one side.
These features are particularly easy to manufacture in terms of production engineering, for example by way of corresponding molded-on elements if the pump cover is configured as a plastic part. In an overpressure situation the pump cover can then tilt slightly to the side, for example via a molded-on tilting edge, so that the seal of the conveying chamber between inlet and outlet is broken and the pump conveys from the inlet through the resulting opening back toward the inlet. When the overpressure situation no longer exists, the plunger pushes the pump cover back again and the seal once again exists, so that the pump then conveys from the intake side to the delivery side.
In a further embodiment of the invention, there is received in the drive body a pressure sensor which communicates with the outlet via a membrane and a stub line.
This feature has the advantage that the components which may be mechanically somewhat more complex, such as the pressure sensor, can be received in the drive body in a manner hermetically sealed off with respect to the pump body, and thus do not need to be disassembled, cleaned, and sterilized after use. Technically complex pressure monitoring and overpressure control systems can thus also be provided without impairing the simple configuration of the actual pump body, with the advantages described previously.
In a further embodiment of the invention, the helical tooth set is configured as a herringbone tooth set.
This feature has the advantage that the herringbone tooth set can create a particularly intensive engagement at multiple points on the meshing gears, and the herringbone arrangement makes possible particularly good sealing between the gears and compensates for axial forces.
It is understood that the features mentioned above and those yet to be explained below can be used not only in the respective combinations indicated, but also in other combinations or in isolation, without leaving the context of the present invention.